DecoratedCache.putForExternalRead method with Metadata ignores Metadata

The implementation of the putForExternalRead method ignores the Metadata parameter, instead of passing it on to the putForExternalRead method in the cache implementation. This is no doubt because the cache implementation previously didn't support Metadata for putForExternalRead.

I will prepare a PR and attach it to this ticket shortly. It was a gargantuan effort to patch this up, as you'll see!